1. Field of the Invention
The present invention relates generally to photography, and more particularly to shutter release mechanisms for cameras.
2. Description of the Prior Art
Those versed in the prior art dealing with shutter release mechanisms for still picture cameras are aware of the lost motion or free play which may be sensed by the camera operator during the initial stage of manually depressing a shutter release member to initiate actuation of the camera shutter. This lost motion often takes the form of a lag between the movement of the shutter release member and that of a restraining member which is movable by the release member to free the camera shutter or a shutter drive member for actuation. While at times such lost motion may be intentionally provided for in a shutter release mechanism, for example, to enable initial depression of the shutter release member to cause a visible signal to be displayed when the level of available light is unsuitable for a proper exposure; at other times such lost motion is not desired, for example, where design compactness is necessary as in a short-stroke shutter release mechanism or in a compact or pocket-type camera. With prolonged use of the shutter release mechanism, the measure of lost motion or lag between the successive movements of the shutter release member and the restraining member ordinarily increases owing to the wear between contacting surface portions of these members. Such wear, therefore, can cause delayed shutter actuation and may eventually result in mechanical failure of the shutter release mechanism.
When it is desired to prevent actuation of the camera shutter, usually to avoid double exposure or because the level of available light is unsuitable for a proper exposure, it is known to either lock the shutter release member to prevent its manual depression or to display a visible signal in the camera viewfinder during the initial stage of manually depressing the shutter release member. However, there are general disadvantages to these designs. In the first instance, the release lock increases the chance of camera damage through undue pressure being applied to the release member by the camera user; whereas, in the second instance, the use of a visible signal is not a positive means of preventing shutter actuation. One recent design which may avoid these disadvantages is disclosed in U.S. Pat. No. 3,690,228, granted Sept. 12, 1972, in the names of Yamashita et al. According to the Yamashita patent, a shutter release member is normally connected by way of an interlocking member to a latch member which operates to restrain a shutter drive member. During the initial stage of manually depressing the shutter release member, the position of an exposure meter pointer is detected by mechanical means. If the pointer is located outside an automatic exposure range, the interlocking member is disconnected from the shutter release member and the latch member. As a result, the release member cannot actuate the camera shutter even though it is still able to be depressed. While this more recent design may be considered in some ways to represent an improvement over the other prior art examples discussed, it is subject to mechanical failure because of the detailed mechanical relation between the exposure meter pointer and the means for disconnecting the interlocking member from the shutter release and latch members.